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Slicing Java Programs that Throw and Catch Exceptions

Slicing Java Programs that Throw and Catch Exceptions. Matthew Allen Susan Horwitz University of Wisconsin-Madison PEPM 2003 San Diego, CA June 7, 2003. Motivation. Exceptions: Important error-handling technique BUT: Current program-slicing algorithms don’t handle exceptions Goal:

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Slicing Java Programs that Throw and Catch Exceptions

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  1. Slicing Java Programs thatThrow and Catch Exceptions Matthew Allen Susan Horwitz University of Wisconsin-Madison PEPM 2003 San Diego, CA June 7, 2003

  2. Motivation • Exceptions: • Important error-handling technique • BUT: • Current program-slicing algorithms don’t handle exceptions • Goal: • Extend System Dependence Graph (SDG) based slicing to support exceptions Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  3. Outline • Motivation • Program Slicing • Slicing with the SDG • Extending SDG-Based Slicing to Handle Exceptions • Related Work • Conclusions Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  4. Program Slicing • A slice from a component S is the set of components that might affect: • Whether or how often S executes • The value of a variable used at S Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  5. Slicing Example • int x, y; • void foo() { • fact(); • print(x); • print(y); • } • void fact() { • x = 1; • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  6. Slicing Example • int x, y; • void foo() { • fact(); • print(x); • print(y); slice from here • } • void fact() { • x = 1; • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  7. Slicing Example • int x, y; • void foo() { • fact(); • print(x); • print(y); slice from here • } • void fact() { • x = 1; • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  8. Slicing Programs with Exceptions • Exceptions can affect: • Whether or how often a statement executes • Value of a variable used at a statement Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  9. Example: when/how often stmt executes • void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  10. Example: when/how often stmt executes • void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”);  Slice from here • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  11. Example: when/how often stmt executes • void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”);  Slice from here • } • } • void fact() throws NegEx{ • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  12. Exception affects value of variable • void foo() { • try { • fact(); • print(x); • } • catch (NegEx e) { • print(x); • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  13. Exception affects value of variable • void foo() { • try { • fact(); • print(x); • } • catch (NegEx e) { • print(x); Slice from here • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  14. Exception affects value of variable • void foo() { • try { • fact(); • print(x); • } • catch (NegEx e) { • print(x); Slice from here • } • } • void fact() throws NegEx{ • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  15. Exception affects value of variable • void foo() { • try { • fact(); • print(x); • } • catch (NegEx e) { • print(x); Slice from here • } • } • void fact() throws NegEx{ • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  16. Exception affects value of variable • void foo() { • try { • fact(); • print(x); Slice from here • } • catch (NegEx e) { • print(x); • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  17. Exception affects value of variable • void foo() { • try { • fact(); • print(x); Slice from here • } • catch (NegEx e) { • print(x); • } • } • void fact() throws NegEx{ • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  18. Outline • Motivation • Program Slicing • Slicing with the SDG (no exceptions) • Extending SDG-Based Slicing to Handle Exceptions • Related Work • Conclusions Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  19. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } print(x) print(y) exit foo while (y > 0) x = x * y enter foo CFGPDGSDG F T call fact enter fact F T x = 1 F T y-- exit

  20. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } print(x) print(y) exit foo while (y > 0) x = x * y enter foo y = y_in CFGPDGSDG F T y_in = y call fact x = x_out y = y_out enter fact y = y_in F T x = 1 F T y-- x_out = x y_out = y exit

  21. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } call fact T T T T enter foo T T T print(x) y_in = y x_out=x y_out=y x = x_out y = y_out print(y) enter fact x = x * y T T T T T y = y_in y=y_in T T y-- x = 1 while (y > 0) CFGPDGSDG Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  22. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } call fact enter foo print(x) y_in = y y_out=y x_out=x x = x_out y = y_out print(y) enter fact x = x * y y = y_in y=y_in y-- x = 1 while (y > 0) CFGPDGSDG Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  23. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } call fact enter foo print(x) y_in = y y_out=y x_out=x x = x_out enter fact x = x * y y = y_in y=y_in y-- x = 1 while (y > 0) CFGPDGSDG print(y) y = y_out Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  24. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } enter foo call fact call fact y = y_in enter foo print(x) y = y_out y_in = y y_in = y y_out=y x_out=x x = x_out enter fact x = x * y y = y_in y=y_in y-- x = 1 while (y > 0) CFGPDGSDG print(y) y = y_out Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  25. static void foo() { fact(); print(x); print(y); } static void fact() throws NegEx { x = 1; while (y > 0) { x = x * y; y--; } } enter foo call fact call fact y = y_in enter foo print(x) y = y_out y_in = y y_in = y y_out=y x_out=x x = x_out enter fact enter fact x = x * y y = y_in y=y_in y_out=y y=y_in while (y > 0) y-- x = 1 while (y > 0) y-- CFGPDGSDG print(y) y = y_out Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  26. Outline • Motivation • Program Slicing • Slicing with the SDG • Extending SDG-Based Slicing to Handle Exceptions • Related Work • Conclusions Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  27. Example Revisited • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”);  Slice from here • } • } • static void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  28. enter foo y=y_in try call fact normal return catch (NegEx e) y_in=y x=x_out y=y_out print (“no error”) print (“error”) enter fact y=y_in x=1 if(y<0) x_out=x y_out=y throw new NegEx() while (y>0) normal exit NegEx exit x=x*y y-- Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  29. enter foo catch (NegEx e) if(y<0) throw new NegEx() NegEx exit y=y_in try call fact normal return catch (NegEx e) y_in=y x=x_out y=y_out print (“no error”) print (“error”) enter fact y=y_in x=1 if(y<0) x_out=x y_out=y throw new NegEx() while (y>0) normal exit NegEx exit x=x*y y-- Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  30. static void fact() • throws NegEx • { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  31. enter fact y = y_in throw new NegEx() x=1 if(y<0) while (y>0) x=x*y y-- F T • static void fact() • throws NegEx • { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } F T F T x_out = x y_out = y exit Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  32. enter fact y = y_in throw new NegEx() x=1 if(y<0) while (y>0) x=x*y y-- F T • static void fact() { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } F T NegEx exit F T x_out = x y_out = y exit Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  33. enter fact y = y_in throw new NegEx() NegEx exit x=1 if(y<0) while (y>0) x=x*y y-- F T • static void fact() { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } F T F T normal exit x_out = x y_out = y exit Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  34. enter fact y = y_in throw new NegEx() NegEx exit x=1 if(y<0) while (y>0) x=x*y y-- normal exit F T • static void fact() { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } F T F T F T x_out = x y_out = y exit Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  35. enter fact y = y_in throw new NegEx() NegEx exit x=1 if(y<0) while (y>0) x=x*y y-- normal exit F T • static void fact() { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } F T F T F T x_out = x y_out = y exit Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  36. enter foo try y = y_in call fact catch (NegEx e) print (“no error”) print (“error”) x_out = x y_out = y exit • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  37. enter foo try y = y_in call fact print (“no error”) print (“error”) x_out = x y_out = y exit • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } normal NegEx normal return catch (NegEx e) Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  38. enter foo try y = y_in call fact normal return catch (NegEx e) print (“no error”) print (“error”) x_out = x y_out = y exit • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } normal NegEx F F T T Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  39. enter foo try y = y_in call fact normal return catch (NegEx e) print (“no error”) print (“error”) x_out = x y_out = y exit • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } F T normal NegEx F F T T Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  40. enter foo try y = y_in call fact normal return catch (NegEx e) print (“no error”) print (“error”) x_out = x y_out = y exit • static void foo() { • try { • fact(); • print(“no error”); • } • catch (NegEx e) { • print(“error”); • } • } F T normal NegEx F F T T Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  41. Example revisited • static void foo() { • try { • fact(); • print(x); • } • catch (NegEx e) { • print(x); Slice from here • } • } • static void fact() { • x = 1; • if (y < 0) • throw new NegEx (); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  42. enter foo try x=x_out call fact normal return catch (NegEx e) enter fact x=1 if(y<0) throw new NegEx() while (y>0) normal exit x_out=x x=1 NegEx exit x=x*y y-- x=x*y y=y_in y_in=y y=y_out x=x_out print(x) print(x) y=y_in x_out=x y_out=y Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  43. enter foo try call fact normal return catch (NegEx e) print(x) print(x) enter fact x=1 if(y<0) throw new NegEx() while (y>0) normal exit NegEx exit x=x*y y-- y=y_in y_in=y x=x_out y=y_out x=x_out y=y_out y=y_in y_out=y x_out=x y_out=y x_out=x

  44. enter foo try call fact normal return catch (NegEx e) x=x_out y=y_out y=y_out x=x_out print(x) enter fact x=1 x=1 if(y<0) x_out=x x_out=x y_out=y y_out=y throw new NegEx() while (y>0) normal exit NegEx exit x=x*y y-- x_out=x y=y_in y_in=y x=x_out print(x) y=y_in

  45. enter foo normal return y=y_out y=y_out x=x_out print(x) x=1 x_out=x y_out=y y_out=y while (y>0) normal exit x=x*y y-- x_out=x y=y_in try call fact catch (NegEx e) y_in=y x=x_out print(x) enter fact y=y_in if(y<0) throw new NegEx() NegEx exit

  46. Other Issues • finally clauses • Unchecked exceptions • See paper! Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  47. Outline • Motivation • Program Slicing • Slicing with the SDG • Extending SDG-Based Slicing to Handle Exceptions • Related Work • Conclusions Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  48. Related Work • [Sinha / Harrold / Rothermel 1999] • Addresses slicing programs with exceptions. • Some similar aspects . • Problems: • Does not correctly represent interprocedural control dependences when length of call chain from try to throw is greater than 1. • Does not address data dependences. • [Sinha / Harrold 1998, 2000] • Addresses handling finally clauses. • See paper. Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  49. Conclusions • Slicing is an important operation. • Slicing Java programs is an area of current interest. • Contribution: • Extend SDG-based Slicing: • To correctly handle exceptions. • Changes only to CFG. • Same slicing algorithm! Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

  50. Example: when/how often stmt executes • void foo() { • try { • fact(); • print(“no error”); Slice from here • } • catch (NegEx e) { • print(“error”); • } • } • void fact() throws NegEx { • x = 1; • if (y < 0) • throw new NegEx(); • while (y > 0) { • x = x * y; • y--; • } • } Slicing Java Programs that Throw and Catch Exceptions – Allen / Horwitz

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